Dynamic Array Allocation

Dynamic Array Allocation Program in C++

BeginnerTopic: Memory Management Programs
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C++ Dynamic Array Allocation Program

This program helps you to learn the fundamental structure and syntax of C++ programming.

Try This Code
#include <iostream>
using namespace std;

int main() {
    int size;
    
    cout << "Enter array size: ";
    cin >> size;
    
    // Dynamically allocate array
    int* arr = new int[size];
    
    cout << "Enter " << size << " elements: ";
    for (int i = 0; i < size; i++) {
        cin >> arr[i];
    }
    
    cout << "\nArray elements: ";
    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
    
    // Calculate sum
    int sum = 0;
    for (int i = 0; i < size; i++) {
        sum += arr[i];
    }
    
    cout << "Sum: " << sum << endl;
    cout << "Average: " << (double)sum / size << endl;
    
    // Find max and min
    int max = arr[0], min = arr[0];
    for (int i = 1; i < size; i++) {
        if (arr[i] > max) max = arr[i];
        if (arr[i] < min) min = arr[i];
    }
    
    cout << "Maximum: " << max << endl;
    cout << "Minimum: " << min << endl;
    
    // Free memory
    delete[] arr;
    arr = nullptr;
    
    return 0;
}
Output
Enter array size: 5
Enter 5 elements: 10 20 30 40 50
Array elements: 10 20 30 40 50
Sum: 150
Average: 30
Maximum: 50
Minimum: 10

Understanding Dynamic Array Allocation

This program teaches you how to allocate Dynamic Arrays in C++. Dynamic array allocation allows you to create arrays whose size is determined at runtime, which is essential when the size is not known at compile time. Dynamic arrays are stored on the heap, allowing much larger sizes than stack arrays.

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1. What This Program Does

The program demonstrates dynamic array allocation:

Getting array size from user at runtime
Allocating array using new[]
Reading and processing array elements
Performing operations (sum, average, max, min)
Freeing memory using delete[]

Dynamic arrays enable flexible, runtime-determined data structures.

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2. Header File Used

This header provides:

cout for displaying output
cin for taking input from the user

---

#include <iostream>

3. Understanding Dynamic Arrays

Dynamic Array Concept

:

Size determined at runtime
Allocated on heap (not stack)
Can be much larger than stack arrays
Must be explicitly freed

Advantages

:

Size not fixed at compile time
Can handle large arrays
Flexible memory usage
User-determined sizes

---

4. Allocating Dynamic Array

Basic Allocation

:

int size;

cin >> size;

int* arr = new int[size];

How it works

:

Size obtained from user at runtime
new[] allocates memory for size elements
Returns pointer to first element
Can access like regular array: arr[0], arr[1]

---

5. Reading Array Elements

Input Loop

:

for (int i = 0; i < size; i++) {

cin >> arr[i];

}

How it works

:

Reads elements one by one
Stores in dynamically allocated array
Same syntax as regular arrays
Size can be any value (within memory limits)

---

6. Processing Dynamic Array

Operations

:

Sum: add all elements
Average: sum / size
Max/Min: find largest/smallest

Example

:

int sum = 0;

for (int i = 0; i < size; i++) {

sum += arr[i];

}

double average = (double)sum / size;

How it works

:

Process elements like regular arrays
All standard array operations work
Size is known (stored in variable)

---

7. Freeing Dynamic Array

Deallocation

:

delete[] arr;

arr = nullptr;

How it works

:

delete[] frees entire array
Returns memory to system
Prevents memory leak
Set to nullptr for safety

Important

:

Always use delete[] (not delete)
Must match new[] with delete[]
Forgetting delete[] causes memory leak

---

8. When to Use Dynamic Arrays

Best For

:

Size unknown at compile time
Large arrays (avoid stack overflow)
User-determined sizes
Variable-sized data structures
Runtime configuration

Example Scenarios

:

Reading file data (unknown size)
User input arrays
Large matrices
Dynamic data processing

---

9. Important Considerations

Memory Management

:

Always delete[] what you new[]
Memory leak if not freed
Can cause program to run out of memory
Set pointer to nullptr after deletion

Stack vs Heap

:

Stack arrays: fixed size, limited size
Heap arrays: dynamic size, much larger
Stack overflow for large arrays
Heap allows larger allocations

Size Limitations

:

Heap can handle much larger arrays
Limited by available memory
Stack typically limited to few MB
Heap can use GB (system dependent)

---

10. return 0;

This ends the program successfully.

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Summary

Dynamic arrays: size determined at runtime, allocated with new[].
Stored on heap, allowing much larger sizes than stack arrays.
Access like regular arrays: arr[i] syntax works.
Always free with delete[] (not delete) to prevent memory leaks.
Set pointer to nullptr after deletion for safety.
Understanding dynamic arrays enables flexible, runtime-sized data structures.
Essential for handling user-determined or variable-sized data.

This program is fundamental for learning dynamic memory allocation, understanding heap vs stack, and preparing for advanced data structures and memory management in C++ programs.

Let us now understand every line and the components of the above program.

Note: To write and run C++ programs, you need to set up the local environment on your computer. Refer to the complete article Setting up C++ Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your C++ programs.

Practical Learning Notes for Dynamic Array Allocation

This C++ program is part of the "Memory Management Programs" topic and is designed to help you build real problem-solving confidence, not just memorize syntax. Start by understanding the goal of the program in plain language, then trace the logic line by line with a custom input of your own. Once you can predict the output before running the code, your understanding becomes much stronger.

A reliable practice pattern is to run the original version first, then modify only one condition or variable at a time. Observe how that single change affects control flow and output. This deliberate style helps you understand loops, conditions, and data movement much faster than copying full solutions repeatedly.

For interview preparation, explain this solution in three layers: the high-level approach, the step-by-step execution, and the time-space tradeoff. If you can teach these three layers clearly, you are ready to solve close variations of this problem under time pressure.

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